The inventor of the present application has previously developed various screwdrivers. They are constructed so that an anchoring pin is disposed on the blade tip of the screwdriver, and the blade tip and the slot of the screw head are engaged and caused to adhere tightly to each other utilizing the elastic force of the anchoring pin, as a means for attaching and holding the screw head in the blade tip of the screwdriver when the blade tip of the screwdriver is engaged with the slot formed in the screw head, transporting the screwdriver and screw to a desired position, and securely performing a screw-in operation. The applicant has obtained patents for these screwdrivers (Japanese Patent Application Publication (Kokoku) No. S46-31719, Japanese Patent Application Publication (Kokoku) No. S47-596 and Japanese Patent Application Publication (Kokoku) No. S48-9440).
Screwdrivers equipped with a such screw holding means have a structure in which a blade piece that has a blade holding pin is detachably engaged with a screwdriver bit holder which is provided with a blade piece clamping groove and a blade piece insertion hole formed in its tip end portion. In this structure, the blade piece that has a blade holding pin is provided with a blade piece main portion, which has a broader diameter than the screwdriver bit holder, and a supporting tail portion, which extends while being slightly bent in the side surface from the center of the upper edge; and one end of an elastic pin is fastened to one side surface of the upper end of the supporting tail portion, and the other end of the elastic pin is extended to the vicinity of the lower end of an anchoring projecting portion that is disposed on the center of the lower edge of the blade piece main portion, so that the elastic is separated from the blade piece.
Screwdrivers equipped with a screw holding means constructed as described above are used with special screws which have a slot consisting of a rectilinear groove that is formed in the screw head so that the groove cuts across the center of the screw head and which have an anchoring hole that has a diameter greater than the groove width of the rectilinear groove and is formed in the center of the rectilinear groove. Accordingly, it is difficult to make screwdrivers equipped with a screw holding means of type described above usable on numerous different types of screws that have diverse screw engagement grooves such as the screws that are seen today.
In the past, therefore, a tool, which includes a tubular member, a sliding member, a sliding driving member, a chucking member and a closing direction driving member, has been proposed as a power tool that can cause attachment and detachment with respect to a screw in an accurate, secure, easy and safe manner (Japanese Patent Application Laid-Open (Kokai) No. H7-328946). In this tool, the tubular member is fastened to the non-rotating portion of a power tool that has a rotating shaft that rotates the screw; and the sliding member is engaged with the inner circumferential side of the tubular member so that the sliding member can slide in the axial direction by a specified dimension, and this the sliding member has an axially oriented through-hole into which the rotating shaft of the power tool is inserted. The sliding driving member drives the sliding member in a direction that causes this sliding member to protruded from the tubular member. The chucking member has a spreading screw head guide surface, which is formed on the inside of the tip end, and a screw head gripping surface, which is connected to the rear end of the guide surface and supports the head portion of the screw so that the axial center of the screw coincides with the axial center of the rotating shaft; and this chucking member is attached to the sliding member so that the chucking member can open and close in the direction of its diameter. Furthermore, the closing direction driving member drives the sliding member in the closing direction.
In a power tool constructed in this manner, when the sliding member is caused to move into the tubular member by a specified dimension against the driving force of the sliding driving member, a chucking member consisting of claws disposed in three locations at substantially equal intervals along the outer circumferential surface of the sliding member is locked in a closed state by the tubular member. On the other hand, when the sliding member protrudes from the tubular member in accordance with the driving force of the sliding driving member, the locking of the chucking member is released.
Furthermore, as an alternative, a tool that includes an engaging shaft, a screw holder and an urging means is proposed as a screw holding device for an electric power tool (Japanese Patent Application Laid-Open (Kokai) No. H-8-71939). In this tool, the engaging shaft has a bit attached to the tip end in a detachable manner; and the screw holder is attached to this engaging shaft so that the screw holder can slide but cannot slip off so that at least three elastic holding pieces are disposed in a direction in which the tip ends of these elastic holding pieces open away from each other and the peripheries of these elastic holding pieces are covered by tubular covers that are open at the tip end. In addition, the urging means urges the screw holder in the direction of the tip end of the engaging shaft.
In this screw holding device, when it is coupled to the drive shaft of an electric power tool, and the head of a screw is press-fitted from the tip end opening of the cover of the screw holding device to which a bit corresponding to the tip end is attached, the elastic holding pieces are bent to the outside, so that the screw head rides over the shallow inverted “V” shaped bent portion, and the crew head is inserted to a position in which the screw head engages with the bit. In this state, the elastic holding pieces recover their original shape as a result of their own elastic force and press against the circumference of the neck of the screw, thus holding the screw so that the screw is prevented from slipping out.
However, in the screwdrivers equipped with a conventional screw holding means as described above, not all of these screwdrivers are screwdrivers that hold the screw by being engaged with the bit engagement groove formed in the screw head, and some of these screwdrivers elastically chuck the outer circumference of the screw head or hold the circumference of the neck of the screw by pressing contact using elastic holding pieces. Accordingly, while screwdrivers equipped with the conventional screw holding means are advantageous in that they do not use a magnet, these screwdrivers conversely involve the difficulties. Namely, the shapes and structures of the chucking member or elastic holding pieces are complicated, the number of parts required is large, and some trouble must be taken in order to manufacture these screwdrivers. Moreover, there is also an increase in the manufacturing cost, etc.
The inventor of the present application previously developed a screw and screwdriver bit combination. In this combination, an improvement was made in the structure of the groove in the bit engagement groove formed in the head of a screw, so that the phenomenon of “come-out” of the screwdriver bit is effectively prevented in screw tightening work, thus preventing damage to the screw head of the type seen in conventional screwdrivers, quick and suitable screw tightening work is accomplished even in cases where some damage is generated in the bit engagement groove of the screw, and the working efficiency is extremely high. The inventor filed a patent application for this screw and screwdriver bit combination (Japanese Patent Application Laid-Open (Kokai) No. H8-145024).
In the screw and screwdriver bit combination in the above-described proposal, a vertical end wall with a specified depth is formed in the end edge portion of the bit engagement groove of the screw head, horizontal step portions are respectively formed from the vertical end edge portions, and respective inclined grooves are formed as extensions toward the center of the neck of the screw from these horizontal step portions. Furthermore, a substantially circular conical bottom surface is formed in the bottom, and the screw is combined with a screwdriver bit equipped with a vane that engages with the vicinity of the horizontal step portions.
In the screw constructed in this manner, when the tip end of the screwdriver bit and the bit engagement groove are engaged, the taper contact surface area with respect to the overall bit engagement groove is partial and small; moreover, since the vertical end wall and horizontal step portions are disposed so that the area of the side wall contacted by the tip end of the screwdriver bit in the boundary between adjacent bit engagement grooves is expanded, the advantage of the secure prevention of the phenomenon of “come-out” of the screwdriver bit is obtained. Furthermore, it is also confirmed that in the screw constructed in this manner, since vanes having substantially perpendicular edges that engage with the horizontal step portions formed in the end edges of the bit engagement groove of the screw are respectively disposed, a screwdriver bit that is most suitable for the screw is obtained.
Accordingly, the inventor of the present application, as a result of various investigations and trials, ascertained that a screw holding type screwdriver bit with versatility and a combination thereof with a screw, which are relatively simple in structure and manufactured easily at low cost, can be obtained by a structure that includes: a plurality of blade portions in which substantially perpendicular end edge portions are formed in the tip ends of the blade portions, a part of one of the blade portions being cut out in a direction of the axis of the screwdriver bit; a guide passage which has a specified length and is formed in the screwdriver bit's shaft portion that forms a continuation on a line which is substantially an extension of the cut-out; and an elastic piece inserted and disposed in the guide passage so that the elastic piece elastically contacts a bit engagement groove of the head portion of a screw and has a screw holding function as a result of interaction with blade portions that are inserted into the bit engagement groove.
Accordingly, the object of the present invention is to provide a screw holding type screwdriver bit and a combination thereof with a screw that, by modification of the structure of the blade portion of the screwdriver bit, effectively prevent the phenomenon of “come-out”, have a simple structure and are easy to manufacture at low cost and perform quick and suitable screw tightening work at all times, thus improving the working efficiency conspicuously.